1. Field of the Invention
This invention relates to pneumatically operated expandable winding mandrels, or air shafts, and particularly to air shafts for differentially winding multiple webs simultaneously.
2. Description of the Prior Art
Expandable mandrels are commonly used for winding rolls of web material such as films, foils, and tapes onto cores. After a core, or several cores, is positioned on a mandrel, the mandrel is expanded by a pressurized fluid, usually compressed air, to engage the inside of the core. The pressure is adjusted so that the core will not slip on the mandrel unless a predetermined web tension is exceeded.
Pneumatically actuated expandable mandrels, called air shafts in the industry, typically have one or more thin-walled cylindrical segments, or leaves, fitted around the circumference of a support shaft. The leaves are held to the shaft by spring loaded fasteners that allow the leaves to be urged radially outward upon inflation of one or more resilient tubes extending along the length of the shaft. Alternatively, rows of axially-spaced spring loaded buttons extending the length of the support shaft may be used instead of continuous leaves.
In some designs, there is an inflatable tube provided for each leaf or row of buttons, each tube being disposed in a corresponding longitudinal groove in the outer surface of a support shaft. A simpler arrangement is to provide a single rubber tube in the center of a hollow support shaft. Examples of the latter type of air shaft are shown in U.S. Pat. No. 3,391,878 of N. G. Naccara and also are manufactured by Daven Industries, Inc., the assignee of the present invention.
A common application of air expandable shafts relates to converting wide rolls of web material into multiple narrow strips. The process involves unwinding a wide web from a single long core, slitting the web into narrow strips, and rewinding the strips simultaneously on corresponding narrow cores. Usually, the multiple strips are rewound on two parallel mandrels, each mandrel carrying equally spaced cores for winding alternative strips of the slit web.
Although leaf-type air shafts can be used for multiple core winding in some instances, they do not produce satisfactory results in web converting operations. Due to minor variation in core diameters and web thickness, the several strips will not rewind evenly unless equal tension is maintained in each strip as it rewinds. This requires that the cores be able to slip differentially with respect to each other on the same shaft. It is also important that the cores not move axially on the shaft during winding; otherwise the edges of the rewound strips will not lie precisely in two parallel planes perpendicular to the axis of the core. Air shafts having leaves that extend the full length of the support shaft do not provide the necessary individual slip control for each core and do not prevent the cores from shifting axially.
Consequently, air shafts intended for differential winding of multiple cores customarily have separate axially-spaced expansion members for engaging each core. An example of such a differential winding mandrel is shown in U.S. Pat. No. 3,853,280 of J. V. Pennisi, et al. The Pennisi mandrel has a single row of shouldered arcuate members on one side of a mandrel body. Although relatively simple in design, this arrangement is unsymmetrical and would tend to expand the cores into an out-of-round condition. Also, the mandrel body does not have equal bending stiffness in all radial directions, which could lead to wobble or whip during winding.
Other types of differential winding mandrels are shown in U.S. Pat. No. 4,266,737 of E. A. Mastriani, 4,026,491 of T. Bostroem, 3,817,468 of A. E. Smolderen, et al., 3,904,144 of G. Gattrugeri, 3,552,672 of K. E. L. Grettve and 4,026,488 of K. Hashimoto. These other types are also relatively complicated, have multiple inflatable members, or have other drawbacks.